The development of technologies to determine the position of a mobile device has enabled application developers and wireless network operators to provide location-based and location-aware services. Examples of these are guiding systems, shopping assistance, friend finder, presence services, community and communication services and other information services that give the mobile user information about his or her surroundings or that use this information to enhance their services.
In addition to the commercial services facilitated by these technologies, location-based emergency services are also being deployed. The governments in several countries have put specific requirements on the network operators to be able to determine the position of an emergency call. For instance, governmental requirements in the United States specify that mobile networks must be able to determine the position of a certain percentage of all emergency calls and further include accuracy requirements. The requirements make no distinctions between indoor and outdoor environments.
In many environments, the position can be accurately estimated by using positioning methods based on Global Navigation Satellite Systems (GNSS), such as the well-known Global Positioning System (GPS). However, GPS-based positioning may often have unsatisfactory performance, especially in urban and/or indoor environments.
Complementary positioning methods may also be provided by a wireless network to augment GPS technology. In addition to mobile terminal-based GNSS (including GPS), the following methods are currently available or will be soon be included in the Long-Term Evolution (LTE) standards developed by the 3rd-Generation Partnership Project (3GPP):                Cell ID (CID),        E-CID, including network-based angle-of-arrival (AoA),        Assisted-GNSS (A-GNSS), including Assisted-GPS (A-GPS), based on satellite signals,        Observed Time Difference of Arrival (OTDOA),        Uplink Time Difference of Arrival (UTDOA)—currently being standardized.        
Several positioning techniques are based on time-difference-of-arrival (TDOA) or time-of-arrival (TOA) measurements. Examples include OTDOA, UTDOA, GNSS, and Assisted-GNSS (A-GNSS). A typical, though not the only, format for the positioning result with these techniques is an ellipsoid point with an uncertainty circle/ellipse/ellipsoid, which is the result of intersection of multiple hyperbolas/hyperbolic arcs (e.g., OTDOA or UTDOA) or circles/arcs (e.g., UTDOA, GNSS, or A-GNSS).
Several techniques, such as Adaptive Enhanced Cell Identity (AECID), may involve a mix of any of the methods above, and are thus regarded as “hybrid” positioning methods. With these methods, the position result can be almost any shape, but in many cases it is likely to be a polygon.
Cellular-based positioning methods (as opposed to satellite-based methods, for example) rely on knowledge of anchor nodes' locations, i.e., the fixed locations from which measured signals are transmitted (e.g., for OTDOA) or the fixed locations at which signals transmitted by mobile devices are measured (e.g., for UTDOA). These fixed locations may correspond, for example, to base station or beacon device locations for OTDOA, Location Measurement Unit (LMU) antenna locations for UTDOA, and base station locations for E-CID. The anchor nodes' locations may also be used to enhance AECID, hybrid positioning, etc.
Positioning Architecture
In 3GPP, location-based services are known as Location Services (LCS). Three key network elements in an LTE positioning architecture are the LCS Client, the LCS target and the LCS Server. The LCS Server is a physical or logical entity that manages positioning for a LCS target device by collecting measurements and other location information, assists the target device in measurements when necessary, and estimating the LCS target location. A LCS Client is a software-based and/or hardware entity that interacts with a LCS Server for the purpose of obtaining location information for one or more LCS targets, i.e., the entities being positioned. LCS Clients may reside in a network node, an external node (i.e., a network external to a cellular network), a Public Safety Access Point (PSAP), a user equipment (or “UE,” in 3GPP terminology for an end-user wireless station), a radio base station (or “eNodeB,” in LTE systems), etc. In some cases, the LCS Client may reside in the LCS target itself. An LCS Client (e.g., an external LCS Client) sends a request to LCS Server (e.g., a positioning node) to obtain location information. The LCS Server processes and services the received requests and sends the positioning result (sometimes including a velocity estimate) to the LCS Client.
In some cases, the position calculation is conducted by a positioning server, such as an Enhanced Serving Mobile Location Center (E-SMLC) or a Secure User-Plane Location (SUPL) Location Platform (SLP) in LTE. In other cases, the position calculation is carried out by the UE. The latter approach is known as the UE-based positioning mode, while the former approach includes both network-based positioning, i.e., position calculation in a network node based on measurements collected from network nodes such as LMUs or eNodeBs, and UE-assisted positioning, where the position calculation in the positioning network node is based on measurements received from UE.
LTE Positioning Protocol (LPP) is a positioning protocol for control plane signaling between a UE and an E-SMLC, which is used by the E-SMLC to provide assistance data to the UE and by the UE for reporting measurements to the E-SMLC. LPP has been designed in such a way that it can also be utilized outside the control plane domain such as in the user plane in the context of SUPL. LPP is used for downlink positioning.
LTE Positioning Protocol Annex (LPPa), sometimes referred to as LTE Positioning Protocol A, is a protocol between the eNodeB and the E-SMLC, and is specified only for control-plane positioning procedures, although it still can assist user-plane positioning by querying eNodeBs for information. For example, LPPa can be used to retrieve information such as positioning reference symbol (PRS) configuration in a cell for OTDOA positioning, or UE sounding reference signal (SRS) configuration for UTDOA positioning, and/or eNodeB measurements. LPPa may be used for downlink positioning and uplink positioning.
FIG. 1 illustrates the UTDOA architecture currently under discussion in 3GPP, including nodes found in the Radio Access Network (RAN) and the core network, as well as an external LCS Client. Although uplink (UL) measurements may in principle be performed by any radio network node, such as the illustrated LTE eNodeB 110, the UL positioning architecture also includes specific UL measurement units, known as Location Measurement Units (LMUs), which are logical and/or physical nodes that measure signals transmitted by a target UE, such as the UE 130 illustrated in FIG. 1. Several LMU deployment options are possible. For example, referring to FIG. 1, LMU 120a is integrated into eNodeB 110, while LMU 120b shares some equipment, e.g., at least antennas, with eNodeB 110. LMU 120c, on the other hand, is a standalone physical node comprising its own radio components and antenna(s).
While the UTDOA architecture is not finalized, there will likely be communication protocols established for communications between a LMU and positioning node, and there may be some enhancements to support UL positioning added to the existing LPPa or to similar protocols.
In particular, a new interface between the E-SMLC and LMU is being standardized for uplink positioning. This interface, known as SLm, is terminated between a positioning server, e.g., the E-SMLC 140 pictured in FIG. 1, and an LMU. It is used to transport messages according to the SLmAP protocol, a new protocol being specified for UL positioning, between the E-SMLC and the LMU. SLmAP can be used to provide assistance data to an LMU, as discussed in further detail below. This protocol may also be used by the LMU to report to the E-SMLC results of measurements on radio signals performed by the LMU. The SLmAP protocol was previously referred to as the LMUp protocol; thus it should be understood that references herein to SLmAP are referring to a developing protocol referred to as LMUp elsewhere, and vice versa.
In LTE, UTDOA measurements, known as UL relative time-of-arrival (RTOA) measurements, are performed on Sounding Reference Signals (SRS). To detect an SRS signal, an LMU 120 needs a number of SRS parameters to generate an SRS sequence that is correlated against the received signal. These parameters are not necessarily known to LMU 120. Thus, to allow the LMU to generate the SRS sequence and detect the SRS signals transmitted by a UE, SRS parameters must be provided in the assistance data transmitted by the positioning node to LMU; these assistance data would be provided via SLmAP. The specific contents of the assistance data to be provided to LMUs by a positioning node are currently being discussed. It has been proposed that the same parameters should be signaled from the eNodeB to a positioning node.
TABLE 1Parameter CategoryParametersGeneralC-RNTIServing eNB eCGI, PCIUL-EARFCNCyclic prefix ConfigUL-BandwidthSRSBandwidthSub-frame configurationFreguency domain positionCyclic shiftDurationTransmission combConfiguration indexMaxUpPts
Measurements for UL positioning and UTDOA are performed on UL transmissions, which may include, for example, reference signal transmissions or data channel transmissions. UL RTOA is the currently standardized UTDOA timing measurement, and may be performed on Sounding Reference Signals (SRS). The results of the measurements are signaled by the measuring node (e.g., LMU) to the positioning node (e.g., E-SMLC), e.g., over SLmAP.
FIG. 2 illustrates the current architecture under discussion in 3GPP for downlink (DL) positioning, again including nodes found in the Radio Access Network (RAN) and the core network, as well as an external LCS Client. It will be appreciated that this architecture includes many of the same components found in the UL positioning architecture illustrated in FIG. 1. Two additional components shown in FIG. 2, however, are the Serving Gateway (S-GVV) and the Packet Data Network Gateway (PDN GW, or P-GW). These gateways terminate the UE's interfaces towards the E-UTRAN network and the Packet Data Network (PDN), respectively.
LPP is currently used for downlink positioning. An LPP message may also include an LPP extension packet data unit (EPDU); Open Mobile Alliance (OMA) LPP Extensions, defined as LPPe, take advantage of this possibility. Currently, LPP and LPPe are used mainly for downlink positioning, while LPPa may be used both for DL and UL positioning.
Positioning Results
A positioning result is a result of processing of obtained measurements, including Cell IDs, power levels, received radio signal strengths or quality, etc. The positioning result is often based on radio measurements (e.g., timing measurements such as timing advance and RTT or power-based measurements such as received signal strength) received from measuring radio nodes (e.g., UE or eNodeB or LMU).
The positioning result may be exchanged among nodes in one of several pre-defined formats. The signaled positioning result is represented in a pre-defined format, e.g., corresponding to one of the seven Universal Geographical Area Description (GAD) shapes. Currently, a positioning result may be signaled between:                an LCS target, e.g., a UE, and an LCS server, e.g., over LPP protocol;        two positioning nodes, e.g., an E-SMLC or SLP, e.g., over a proprietary interface;        a positioning server (such as an E-SMLC,) and other network nodes, e.g., a Mobility Management Entity (MME), a Mobile Switching Center (MSC), a Gateway Mobile Location Center (GMLC), an Operations and Maintenance (O&M) node, a Self-Organizing Network (SON) node, and/or a Minimization of Drive Tests (MDT) node;        a positioning node and an LCS Client, e.g., between an E-SMLC and a Public Safety Access Point (PSAP), or between an SLP and an External LCS Client, or between an E-SMLC and a UE.Note that in emergency positioning, the LCS Client may reside in a PSAP.Uplink Positioning Measurements        
As the name suggests, measurements for uplink positioning (e.g., UTDOA) are performed on uplink transmissions, which may comprise, e.g., one or more of physical signal or channel transmissions, e.g., reference signal transmissions, random access channel transmissions, Physical Uplink Control Channel (PUCCH) transmissions, or data channel transmissions. Some examples of reference signals transmitted in LTE UL are SRS and demodulation reference signals.
UL Relative Time of Arrival (RTOA) is a currently standardized UTDOA timing measurement. The measurement may be performed on Sounding Reference Signals (SRS), which may be configured for periodic transmissions, typically comprising multiple transmissions but may also be one transmission. SRS transmissions may be triggered by any of the two trigger types:                Trigger type 0: higher layer signaling from eNodeB,        Trigger type 1: via downlink control channel signaling (DCI formats 0/4/1A for FDD and TDD and DCI formats 2B/2C for TDD).        
Other example uplink measurements are the uplink measurements specified in 3GPP TS 36.214. These measurements include measurements of received signal strength, received signal quality, angle-of-arrival (AoA), eNodeB receive-to-transmit (Rx-Tx) timing, relative time-of-arrival (RTOA), and other other measurements performed by radio network nodes (e.g., eNodeB or LMU). Other known measurements are UL TDOA, UL TOA, UL propagation delay, etc.
Multi-Antenna Systems
Multiple-input multiple-output (MIMO) technologies are a range of advanced antenna techniques used to improve the spectral efficiency and thereby boost the overall system capacity. MIMO implies that both the base station and the UE (“user equipment”—3GPP terminology for an end user's wireless device, mobile terminal, mobile station, etc.) employ multiple antennas, although the term is sometimes used in a manner that includes scenarios in which only one end of the radio link uses multiple antennas. MIMO techniques are widely studied and applied in practice for downlink communications, i.e., from the base station to the mobile terminal, and are increasingly under consideration for uplink communications as well, i.e., from the mobile terminal to the base station.
There exist a variety of MIMO techniques or modes, including Per Antenna Rate Control (PARC), selective PARC (S-PARC), transmit diversity, receiver diversity, Double Transmit Antenna Array (D-TxAA), etc. The last of these, D-TxAA, is an advanced version of transmit diversity, which is already used in the Wideband-CDMA (WCDMA) networks developed by members of the 3rd-Generation Partnership Project (3GPP).
Irrespective of the particular MIMO technique under discussion, the notation (M×N) is generally used to represent MIMO configuration in terms of the number of transmit (M) and receive antennas (N). Common MIMO configurations used or currently discussed for various technologies are: (2×1), (1×2), (2×2), (4×2), (8×2) and (8×4). The configurations represented by (2×1) and (1×2) are special cases of MIMO, corresponding to techniques known as transmit diversity and receiver diversity, respectively. The configuration (2×2) will be used in systems that support Release 7 of the 3GPP's specifications for WCDMA. In particular, WCDMA FDD release 7 will support double transmit antenna array (D-TxAA) in the downlink, which is a multiple-input multiple-output (MIMO) technique to enhance system capacity. (See 3GPP TS 25.214, “Physical Layer Procedures (FDD)”.)
The E-UTRAN (“Evolved Universal Terrestrial Radio Access Network,” the air interface of 3GPP's Long Term Evolution (LTE) upgrade path for mobile networks, will support several MIMO schemes, including single-user MIMO (SU-MIMO), in which several spatially multiplexed transmission layers are targeted to or received from a single user terminal, and multi-user MIMO (MU-MIMO), in which each of several spatially multiplexed downlink layers are targeted to different user terminals. MIMO technology has also been widely adopted in other wireless communication standards, such as the IEEE802.16 standards for wireless broadband communications, often referred to as “WiMAX.”
The above-mentioned MIMO modes or other MIMO techniques enable spatial processing of the transmitted and received signals. In general, the spatial diversity provided by these techniques can be used to improve spectral efficiency, extend cell coverage, enhance user data rate, mitigate multi-user interference, etc. However, in practice each MIMO technique provides its own benefits. For instance, receiver diversity (1×2) particularly improves signal coverage. On the other hand (2×2) MIMO, such as D-TxAA, leads to increased peak user bit rate.
Ideally, a 2×2 MIMO scheme may double the data rate. Whether the data rate can actually be doubled in practice depends on whether the spatial channels between the transmitter and receiver are sufficiently uncorrelated, so that the rank of the 2×2 MIMO channel matrix is two. (The rank is the number of independent rows or columns of the matrix.) In general, the average data rate will be lower than two times the data rate achieved in single link conditions.
So far, MIMO techniques have generally been used only for downlink transmission (i.e., from base stations to mobile terminals), and have not been widely employed for uplink communications. The reason is that MIMO techniques may involve higher levels of complexity both in the transmitter and in the receiver, compared to single-input, single-output (SISO) type of transmissions. In the radio-frequency (RF) portion of a mobile terminal, for example, several power amplifiers may be needed for the transmitter, depending on the MIMO scheme and on the number transmit antennas. In the receiver, multiple antennas are necessary, and multiple RF chains may be needed, depending on the MIMO schemes. Moreover, each MIMO scheme introduces an additional complexity in the baseband processing.
The use of multiple power amplifiers is a feasible approach in base stations, particularly macro base stations, because the base station has fewer constrains on form factor and battery life. While these constraints are more important for smaller base stations and radio access points, they may still be less restrictive than for a mobile implementation. However, if MIMO is to be used in uplink transmission, care should be taken in the design of (possibly multiple) power amplifiers, and on battery life. MIMO in uplink will have an impact on the battery life, power consumption, form factor and complexity; hence, it is important to exploit as much as possible the benefits that these techniques can provide.
As in the downlink, different possible multi-antenna techniques can be applied in the uplink. Examples include beam-forming and antenna switching. Depending on whether the receiving eNodeB is equipped with multiple receiving antennas, transmit-diversity (2 transmit antennas, 1 receiving antenna) or Uplink-MIMO (2×2) may be candidates for use. Moreover, possible schemes include open loop or closed loop techniques. Open loop multi-antenna techniques are based on the assumption that the UE does not have information about the uplink channel; hence it cannot exploit this knowledge in order to optimize the transmission weights (i.e., the transmission beam-forming) in order to steer the beam in the direction of the base station. In contrast, in the case of closed loop multi-antenna techniques, the UE has some information about the uplink channel which it can exploit for optimizing the beam-forming vector.
Uplink Transmit Diversity
Uplink transmit diversity is also a special type of uplink multi-antenna transmission. Recently, 3GPP has started work on uplink transmit diversity for Release 11 of the specifications for UTRA systems and on uplink MIMO for Release 11 of the specifications for E-UTRA systems. In the future, the extension of the transmit diversity scheme to more evolved uplink MIMO schemes will be defined for UTRA as well as for E-UTRA.
Conventionally, a UE includes only a single uplink transmit antenna, which is used for all types of uplink transmission. However, high-end UEs may have and use multiple uplink transmit antennas for uplink transmission. This is commonly referred to as uplink transmit diversity. The objective of transmit diversity transmission is to achieve higher uplink data rate and lower UE transmission power by virtue of spatial, angular and temporal diversities.
The most common uplink transmit diversity is based on the use of two uplink transmit antennas. The signals from two or more uplink transmit diversity antennas may be transmitted in different manners in terms of their phases, amplitudes, power levels, etc. This gives rise to different uplink transmit diversity schemes. Some well-known schemes are:                Transmit beam-forming open-loop        Transmit beam-forming closed-loop        Switched-antenna uplink transmit diversity open-loop        Switched-antenna uplink transmit diversity closed-loop        Space-time transmit diversity        
It should be noted that transmit diversity can be regarded as a special case of the MIMO transmission scheme, which can also be used in the uplink. Hence, the embodiments described herein for uplink transmit diversity can be extended or applied to any MIMO scheme, and vice-versa.
In any MIMO or transmit diversity scheme, a set of parameters related to MIMO or uplink transmit diversity are regularly adjusted by the UE. The objective is to ensure that the uplink transmission incorporates the desired spatial, temporal or angular diversities. This in turn improves uplink coverage, reduces interference, increases uplink bit rate and enables UE to lower its transmitted power.
The MIMO or transmit diversity parameters may comprise: relative phase, relative amplitude, relative power, relative frequency, timing, absolute or total power of signals transmitted on transmit diversity branches, etc. The adjustment of all or a sub-set of these parameters is fundamental to a transmit beam-forming scheme.
The objective of beam-forming is to direct the uplink transmission or beam towards the desired base station, which is generally the serving base station, although it may also be another radio network node, e.g., a cooperating eNodeB in a CoMP deployment. This allows the serving base station to decode the received signal more easily. Furthermore, high directivity of the beam towards the desired base station reduces the interference towards the neighboring base stations. Similarly, in the case of switched-antenna transmit diversity, transmit diversity parameter implies the selection of the most appropriate transmit antenna (e.g. in terms of radio condition) out of the available transmit diversity branches. By virtue of using the most appropriate antenna for the uplink transmission, the UE can either reduce its power while retaining a given uplink information rate, or increase the information rate while retaining a given output power.
In open-loop MIMO or transmit diversity schemes, the UE autonomously adjusts the uplink transmit diversity parameters without the use of any network transmitted control signaling or commands. These schemes are simpler, although they may not show substantial gain in all scenarios.
On the other hand, in closed-loop MIMO or transmit diversity schemes, the UE adjusts the uplink transmit diversity parameters by making use of a suitable network-transmitted control signaling or commands. These commands or control signaling reflect the uplink quality, e.g., the quality measured at the base station. These commands are signaled to the UE over the downlink. Furthermore, the commands can be sent exclusively to the UE to enable it to adjust the uplink transmit diversity parameters. Alternatively the UE can utilize any existing commands or signaling that are originally intended for other purposes, for deriving the uplink transmit diversity parameters. Examples of implicit signaling or commands are transmit power control (TPC) commands and HARQ ACK/NACK, etc., which are sent to the UE by the base station for uplink power control and uplink HARQ retransmission scheme respectively. The closed-loop schemes have a potential of leading to a larger performance gain than open-loop schemes, due to the use of network control parameters signaled for adjusting the uplink transmit diversity parameters.
MIMO or any transmit diversity scheme can be used in any technology including LTE, WCDMA or GSM. For instance in LTE, the switched antenna uplink transmit diversity is standardized in LTE release 8.
UE and Base Station MIMO Capabilities
Support for uplink and/or downlink MIMO is generally a so-called “UE capability,” since it leads to significantly better performance compared to the baseline scenario (single transmit and receive antenna). Therefore, for UEs supporting MIMO, such capability may be communicated to the network at the time of call setup or doing registration process. In some cases, a network configuration may support more than one MIMO mode. In one scenario, a particular base station may support all possible MIMO modes allowed by the corresponding standard. In another scenario the base station may offer only a sub-set of MIMO modes. In a basic arrangement, a base station may not offer any MIMO operation, i.e., it supports only single transmit antenna. Therefore, the actual use of a particular MIMO technique is possible in scenarios where both the serving base station and UE bear the same MIMO capability.
Uplink and/or downlink MIMO can also work in conjunction with multi-carrier. The MIMO with multi-carrier is a different type of UE capability reported to the network.
Multi-Carrier or Carrier Aggregation
To enhance peak rates within a technology, so-called multi-carrier or carrier aggregation solutions are known. Each carrier in multi-carrier or carrier aggregation system is generally termed as a component carrier, or sometimes referred to as a cell. In simple terms, the component carrier is an individual carrier in a multi-carrier system. The term carrier aggregation is also referred to with the terms (e.g., interchangeably called) “multi-carrier system”, “multi-cell operation”, “multi-carrier operation”, “multi-carrier” transmission and/or reception. Carrier aggregation is used for transmission of signaling and data in the uplink and downlink directions. One of the component carriers is the primary component carrier (PCC) or simply primary carrier or even anchor carrier. The remaining ones are called secondary component carriers (SCCs) or simply secondary carriers or even supplementary carriers. Generally the primary or anchor component carrier carries the essential UE specific signaling. The primary component carrier exists in both uplink and downlink direction in carrier aggregation. The network may assign different primary carriers to different UEs operating in the same sector or cell.
With carrier aggregation, the UE has more than one serving cell in downlink and/or in the uplink: one primary serving cell and one or more secondary serving cells operating on the PCC and SCCs respectively. The serving cell is interchangeably called the primary cell (PCell) or primary serving cell (PSC). Similarly, the secondary serving cell is interchangeably called the secondary cell (SCell) or secondary serving cell (SSC). Regardless of the terminology, the PCell and SCell(s) enable the UE to receive and/or transmit data. More specifically the PCell and SCell exist in downlink and uplink for the reception and transmission of data by the UE. The remaining non-serving cells are called neighbor cells.
Component carriers belonging to the CA may belong to the same frequency band (intra-band carrier aggregation) or to different frequency bands (inter-band carrier aggregation) or any combination thereof (e.g., two component carriers in band A and one component carrier in band B). Furthermore, the component carriers in intra-band carrier aggregation may be adjacent or non-adjacent in the frequency domain (intra-band, non-adjacent carrier aggregation). A hybrid carrier aggregation comprising any two of intra-band adjacent, intra-band non-adjacent and inter-band aggregations is also possible. Using carrier aggregation between carriers of different technologies is also referred to as “multi-RAT carrier aggregation” or “multi-RAT-multi-carrier system” or simply “inter-RAT carrier aggregation”. For example, carriers from WCDMA and LTE may be aggregated. Another example is the aggregation of carriers from LTE Frequency-Division Duplex (FDD) and LTE Time-Division Duplexing (TDD) modes, which may also be interchangeably called as multi-duplex carrier aggregation system. Yet another example is the aggregation of LTE and CDMA2000 carriers. For the sake of clarity, carrier aggregation within the same technology as described can be regarded as ‘intra-RAT’ or simply ‘single RAT’ carrier aggregation.
The component carriers in carrier aggregation may or may not be co-located in the same site or radio network node (e.g., a radio base station, relay, mobile relay, etc.). For instance, the component carriers may originate at different locations (e.g., from non-co-located base stations, or from base stations and a remote radio head (RRH), or at remote radio units (RRUs)). Well-known examples of combined carrier aggregation and multi-point communication techniques include the Distributed Antenna System (DAS), the Remote Radio Head (RRH), the Remote Radio Unit (RRU), and Coordinated Multipoint (COMP) transmission. The techniques described herein also apply to multi-point carrier aggregation systems as well as to multi-point systems without carrier aggregation. The multi-carrier operation may also be used in conjunction with multi-antenna transmission. For example signals on each component carrier may be transmitted by the eNodeB to the UE over two or more antennas.
A general problem with current uplink positioning techniques is that the positioning measurements and techniques are defined with respect to single-antenna transmissions. Accordingly, improved techniques for uplink positioning techniques are needed.